The present invention relates to the field printed loop antennas having high gain and wide band width.
Printed circuit antennas are used in a variety communication systems and in particular in mobile communication systems because of their ease of manufacture, low cost, low weight, small volume and flush mount configurations.
Loop Antennas are relatively well known and often used for purposes of radio direction finding (RDF). Such antennas are described generally in xe2x80x9cAntenna engineering hand bookxe2x80x9d Chapter 5, McGraw Hill (2d, Ed. 1984) by R. C. Johnson and H. Jasik Loop Antennas are most useful as elements of directional antennas when there perimeter is comparable to one wavelength. The loop antenna has further attractive characteristic in that the antenna is small enough compared with the operating wavelength.
On the other hand, printed loop antennas combine the advantages of printed circuit antennas and loop antennas. For example, back in the early 1990""s, a reflector loop antenna was proposed by M. Cai and M. Ito in an article entitled xe2x80x9cNew type of printed polygonal loop antenna; IEE proceedingsxe2x80x94H, vol. 138 no. 5, October 1991, pp. 389-396xe2x80x9d. Further loop antenna configurations for printed wire board applications are described in U.S. Pat. No. 6,067,052.
Given the rapid development of wireless communication systems, there is a need for a printed loop antenna having extremely high gain and which is particularly useful in applications requiring embedded antennas. A drawback of conventional loop antennas in these applications is that they are commonly fed from one of there sides; therefore; a symmetry in the radiation pattern is caused by the feed network resulting in a squinted radiation pattern.
There is thus a need for a printed loop antenna which mitigates at least some of the above disadvantages of conventional loop antennas.
In accordance with this invention there is provided a printed loop antenna comprising:
a) a first and second rectangular loop arrange symmetrically on either side of centre feed line; and
b) a feed network is coupled to feed both loops, thereby defining a single element antenna.
In accordance with another aspect of the invention, each of the loops comprise parallel portions defining four dipoles polls and which when properly spaced and excited in phase, generate a high gain.
The antenna of the present invention also exhibits more than 20% bandwidth as portions of the loop provide multiple paths for the surface current of the antenna.
In accordance with a further aspect of the inventions a metal reflector is arranged in one plane of the antenna to provide a directional radiation pattern.
In a still further aspect of the invention a plurality of the individual antennas may be combined to form a two element and eight element array.